Does a person’s criminal behaviour induce others to commit crime? This column exploits the fact that young fathers in Denmark are less likely to continue their criminal careers if their new-born child is a boy rather than a girl to identify spillovers in criminal behaviour. The analysis shows that neighbourhood peers of new fathers of boys become less likely to commit crime themselves than neighbourhood peers of new fathers of girls. The findings suggest that the benefits of programmes that reduce crime at a younger age are far larger than suggested by the primary effects alone.

The propensity for youths to commit crime has long been associated with where they live. This column looks at how the school they attend can shape this relationship. Exploiting changes to school catchment areas in a US school district, it shows that concentrations of students with similar characteristics and from similar neighbourhoods at the same school increase arrest rates, if these potential peers live close to each other. Moreover, youths who live near each other and are in the same school and grade are more likely to commit crimes together. Policies to decrease segregation in schools could thus be effective in reducing crime.

Bad behaviour by peers is well-known to worsen educational outcomes in the short run. This column investigates the long-run effects of peers from families marked by domestic violence. Individual-level US data linking middle and high school test scores, college enrolment, and earnings at ages 24–28 show that students exposed to more disruptive peers experience worse adult outcomes. Policies that mitigate exposure to disruptive peers could pay high dividends.